1. Field of the Invention
The present invention relates to a communication technology, and it particularly relates to a radio apparatus that receives a packet signal containing predetermined information.
2. Description of the Related Art
Road-to-vehicle communication has been under investigation in an effort to prevent collision accidents of vehicles on a sudden encounter at an intersection. In a road-to-vehicle communication, information on conditions at an intersection is communicated between a roadside unit and an in-vehicle unit. Such a road-to-vehicle communication requires installation of roadside units, which means a great cost of time and money. In contrast to this, an inter-vehicular communication, in which information is communicated between in-vehicle units, has no need for installation of roadside units. In that case, current position information is detected in real time by GPS (Global Positioning System) or the like and the position information is exchanged between the in-vehicle units. Thus it is determined on which of the roads leading to the intersection the driver's vehicle and the other vehicles are located. Also, pedestrians carry radio apparatuses to prevent collision accidents between vehicles and pedestrians. Further, the degree of risk is determined from the GPS information on the pedestrians and the vehicles and then the pedestrians and the drivers are informed of the thus determined degree of risk.
It is also desired that not only the collision accidents of vehicles but also the collision accidents between vehicles and pedestrians be prevented. In order to prevent the collision accidents of vehicles, the collision of packet signals between the inter-vehicular communication and the road-to-vehicle communication needs to be suppressed. At the same time, in order to prevent the collision accidents between vehicles and pedestrians, a radio apparatus is carried by a pedestrian, who is an elementary school child, for instance. Since the radio apparatus carried by a pedestrian is battery-powered, the presence of the pedestrian cannot be conveyed to a driver if the remaining battery level gets low.